From: Jim Weirich <jim@...>
Date: 2004-06-22T11:57:29+09:00
Subject: Re: Rake and timestamps (ideoms or methods?)

Phil Tomson wrote:

> If I don't want to run certain tasks if the file the task is to work on 
> already is up-to-date (like how make works) how do I tell Rake to not 
> execute a particular task if the files being worked on are up-to-date?  

Normal tasks don't look at timestamps.  If the goal of a task is to 
create a file, then use a "file" task rather than a "task" task.  File 
tasks will not trigger if the file named by the task is up to date with 
its dependents (which should also be file tasks ... a file task is 
always out of date if it depends on a regular task ... think about it).

So a simple file task declaration could look like:

    file "copy_of_a.txt" => ["a.txt"] do
      cp "a.txt", "copy_of_a.txt"
    end

Translation: The copy depends on the original.  If the original changes, 
then copy the original into the copy.

> Also, notice the 'raise "blah" system("command")' that I'm doing above. 

As long as your external programs exit with status 0 for normal and 
non-zero for errors, then rake will automatically abort.  The explicit 
tests and raises aren't needed

 > Here's my rakefile:

And here's my translation.  I didn't understand everything you were 
doing, so I made some of the following up.  But you should be able to 
translated it into something appropriate.

I assume that ncvhdl is some compiler-like script and the .vhd file is 
the input.  I'm assuming that the output file will be a .vhdo file.

I don't know what ncdlab does, so I just made it a normal task.  It will 
run every time this way.

Here's the file --------------------------------------------------------

#!/usr/bin/env ruby

# This adds a :clean and :clobber target to your Rakefile.
# We also add all intermediate .vhdo files to the clobber target.
require 'rake/clean'
CLOBBER.include("*.vhdo")

# Lets make a list of all the .vhd source files in the directory.

VHD_FILES = FileList['*.vhd']

# And now use that to make a list of all the .vhdo file we
# want to generate.

VHDO_FILES = VHD_FILES.sub(/$/, 'o')

# No change to this task

task :default => [ :sim_jtag_tb ] do
   puts "done..."
end

# I use "sh" instead of system.  "sh" understands
# when to echo commands in Rake.

task :sim_jtag_tb => [ :build_jtag_tb ] do
   puts "simulate it..."
   sh %{ncsim -gui jtag_tb:jtag_tb_behavior}
end

# I don't know what ncdlab does, but I'm assuming it needs
# all the .vhdo files to be present before it can run, so
# we make a dependency.  Fortunately, we already calculated
# the list of .vhdo files. (Note: If I know what kind of output
# file was produced in this step, I would make this a file task
# with the name of the output file.)

task :build_jtag_tb => VHDO_FILES do
   puts "build jtag_tb"
   sh %{ncdlab jtag_tb:jtag_tb_behavior -access +r+w}
end

# Here follows the three files that are processed by ncvhdl.
# The jtag_tb_c was bundled with :build_jtag_tb task before,
# but it looks to me like it could be broken out. (I could
# be wrong.)   Notice the "output file depends on input file"
# pattern.

file "jtag_tb_c.vhdo" => ["jtag_tb_c.vhd"] do
   puts "build jtag_tb_c"
   sh %{ncvhdl -linedebug jtag_tb_c.vhd}
end

file "jtag_driver.vhdo" => ["jtag_driver.vhd"] do
   puts "build jtag_driver"
   sh %{ncvhdl -linedebug jtag_driver.vhd}
end

file "jtag.vhdo" => ["jtag.vhd"] do
   puts "build jtag..."
   sh %{ncvhdl -linedebug jtag.vhd}
end

End of Rakefile-------------------------------------------------

There is a lot of duplication in those last three file tasks.  You could 
  iterate over VHD_FILES and create the file tasks in a loop.  A simpler 
way is to write a rule that describes how to turn .vhd files into .vhdo 
files, e.g.

   rule ".vhdo" => [".vhd"] do |t|
     puts "build #{t.source}"
     sh %{ncvhdl -linedebug #{t.source}}
   end

Use that single rule in place of the final three file tasks.  Here is 
the output from the mockup I did...

----------------------------------------------------
$ rake
(in /home/jim/pgm/misc/philtomson)
build jtag.vhd
ncvhdl -linedebug jtag.vhd
Creating jtag.vhdo
build jtag_driver.vhd
ncvhdl -linedebug jtag_driver.vhd
Creating jtag_driver.vhdo
build jtag_tb_c.vhd
ncvhdl -linedebug jtag_tb_c.vhd
Creating jtag_tb_c.vhdo
build jtag_tb
ncdlab jtag_tb:jtag_tb_behavior -access +r+w
simulate it...
ncsim -gui jtag_tb:jtag_tb_behavior
done...
$
$
$ rake clobber
(in /home/jim/pgm/misc/philtomson)
rm -r jtag.vhdo
rm -r jtag_driver.vhdo
rm -r jtag_tb_c.vhdo
----------------------------------------------------

I hope this helps.

-- 
-- Jim Weirich    jim@weirichhouse.org     http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)